Marine structure



Sept. 13, 1966 K. A. BLENKARN 3,271,963

MARINE STRUCTURE Filed Feb. 13, 1964 INVENTOR.

ATTORNEY.

- 1 -r j KENNETH A. BLENKARN United States Patent M 3,271,963 MARINESTRUCTURE Kenneth A. Blenkarn, Tulsa, Okla, assignor to Pan AmericanPetroleum Corporation, Tulsa, Okla., a corporation of Delaware FiledFeb. 13, 1964, Ser. No. 344,645 2 Claims. (Cl. 61-46) This inventionrelates to marine structures, and more particularly it relates to animproved offshore well structure for use in locations where forces areimposed on the offshore equipment by moving sheets of ice and the like.

In offshore oil and gas operations, wells may be drilled into formationsunderlying water having a depth ranging from a few feet up to severalhundred feet. After drilling and completing such a well, the wellheadmay be located beneath the water or above the surface, according to theneeds for the particular location. In various instances it is desirableto locate the wellhead above the surface of the water. However, incertain cold- Weather locations, for example, in the Cook Inlet area ofAlaska, flowing sheets of ice present considerable problems in designingand constructing such facilities to withstand the ice forces. It hasbeen found that structures can be constructed to withstand the highlevel forces imposed by the flowing ice. However, it has been observedthat the action of the ice in striking a structure such as a productionplatform, breaking up and moving around it subjects the platform torapidly varying loads. As a result, the platform may vibrate violentlyand continuously as the ice sheets move past it. In respect of thewe]lhead equipment atop a completed well, such vibration is highlyundesirable, since the wellhead equipment may be damaged thereby,causing the release of high-pressure well fluids. Secondly, such violentshaking of the structure causes diificult working conditions.

In marine drilling operations, a conductor pipe may be extended from thesurface of the water to the well for the purpose of guiding equipmentinto the well and for circulating drilling fluid between the well andequipment above the water. A conductor pipe may be employed whendrilling from a platform, or a submersible or jack-up barge. When thewell is to be completed :above water, the conductor pipe may remainconnected to the well and the production wellhead mounted atop theconductor. According to prior art methods, the caisson or jacket isdesigned as a load-bearing structure to withstand any forces imposed onthe structure by moving ice or other floating material and/or to supporta platform above the high water level. to such methods, one or moreconductor pipes placed in such a caisson or jacket have beenstructurally connected to the load-bearing structure by ring supports,cementing or lateral bracing. If such a prior art structure is employedin a location where moving ice must be contended with, the vibration ofthe load-bearing structure by the moving ice will be transferred to theproduction equipment so as to bring about the unwanted vibration of thewellhead and other associated production equipment.

According to the present invention an improved marine structure, inwhich the tendency for vibration of operating equipment is reduced, isprovided by structurally isolating a conduit, such as a conductor pipe,positioned inside a large diameter protective tubular member, so thatthe lateral movement of the protective member is not transferred to theinner conduit.

The present invention provides a marine structure comprising a largediameter loadabearing tubular member having its lower end affixed to aformation underlying a body of water and extending upwardly from saidformation to a point above the surface of the water; a conduit However,according 327L963 Patented Sept. 13, 1966 member having its lower endconnected to a well in the underwater formation and extendingupwa-rdlyfrom the well to above the surface of the water; a wellhead assemblymounted on the conduit member above the surface of the water; saidsecond tubular member being positioned inside the large diameter memberand structurally isolated therefrom continuously above a point adjacentthe formation. The large diameter tubular member may be a single caissonor a leg of a platform jacket, and one or more conduit members may bepositioned inside of the large diameter member, as in the case wheremultiple wells are drilled through a single platform leg.

The present invention will be better understood by reference to thefollowing description of the invention and to the accompanying drawingwhich schematically illustrates a partial view of a production platformin accordance with the invention.

Referring to the drawing, a large diameter load-bearing tubular member11 is aflixed to a formation 12 underlying a body of water 13. Thislarge-diameter member is capable of withstanding the ice forces and ofsupporting a platform 15, if desired. In the instance where a caisson isemployed, the caisson may be aflixed to the formation by lowering thecylindrical caisson from the surface of the water to the formation anddriving, jetting or drilling the lower open end of the caisson into thesea ifiOOI to a suitable depth, so that the lower end is stabillizedagainst movement by wind, water or other forces. Also, the caisson isset in the formation to a depth where the caisson is supportedvertically either by bedrock or skin friction. In other instances wherea multilegged platform is employed, a leg of the platform may serve asimilar purpose. In the drawing only one leg of a platform is shown, andof course, the various legs of the platform jacket are usuallystructurally interconnected by members 11a or the like. In suchinstances the platform jacket may be lowered through the water to reston the formation. Generally, it is desirable to aflix the legs of theplatform to the formation by piles extending through the platform jacketlegs into the formation and tying-in the legs to the piles adjacent theformation with a cementitious material. Alternatively, one or moreconductor pipes or casing strings extending into the formation to asuitable depth may be cemented and tied to the platform leg to afiix theplatform leg to the formation.

One or more well conductors 14 extend through the large-diameter tubularmember from the well to above the water. The lower end of each wellconductor typically is driven, jetted or drilled into formation 12 to asuitable depth, and, if desired, may be cemented to the formation,according to well-known techniques. Various methods for setting the wellconductors are Well known in the art and need not be described in detailherein. Inside each well conductor and extending to a desired depth inthe formation there may be positioned one or more casing strings 16extending downwardly into the well. Typically, production tubing 17inside the casing extends from a producing formation in the Wellupwardly through the casing and conductor pipe to a location above theupper end of the large-diameter tubular member, and a wellhead assemblyis secured to the top of the well casing. Typically, the wellheadassembly comprises a control valve 18, choke 19, .and pressure gauge 20.A production flow line 21 leads from the wellhead assembly to storagefacilities (not shown) for accumulating the produced fluids.

The conductor pipe extends upwardly from the well on the inside of thelarge-diameter tubular member and is structurally isolated from thelarge-diameter tubular member continuously above a point adjacent theformation. As mentioned above, the conductor pipe may be structurallytied into the large-diameter member by cement 22 or other means at apoint substantially at the sea floor,

since little movement of the large-diameter member occurs in the areaadjacent the formation. However, at increasing heights above theformation the magnitude of the movement resulting from vibrations causedby the flowing ice increases, and it is increasingly important that theisolation of the well conductor be maintained at increasing distancesabove the sea floor. Further, the spacing between the conductor pipe andthe large-diameter member should be such that the large-diameter memberdoes not contact the well conductor, since such contact can causeunwanted vibrations in the conductor pipe and the wellhead connectedthereto. Advantageously, this spacing is greater than one-half themaximum amplitude of the largediameter member.

Typically, the large-diameter member may be constructed of steel orother suitable material with a wall thickness in the range of about 2 to3 inches and a nominal diameter of about 12 to 16 feet. The conductorpipes typically will have a diameter of about 30 inches, and wheremultiple conductors are installed in a single platform leg, theconductors may be arranged in approximately an 8- to -foot circle sothat the conductors are spaced approximately 3 to 4 feet from theplatform leg.

The conductor pipe installed inside the large-diameter member may beself-supporting, since the conductor pipe is not subjected to anysignificant forces of wind, Water and ice. However, in the case ofmultiple well conductors in a single platform leg, the conductor pipesmay be cross braced by braces 23 serving to connect the conductors toeach other to provide further stability.

If desired, a platform may be attached above the water level to thelarge-diameter tubular member, in which case the structural isolationbetween the well heads and the platform is maintained as described abovein order that vibrations are not transferred to the wellhead. However,if desired, the platform may be connected directly to the top of one ormore conductor pipes, and the above structural isolation maintainedbetween these members and large-diameter member.

While the present invention has been described in terms of a preferredembodiment thereof, it will be understood that from the foregoingdescription various modifications and alterations falling Within thespirit and scope of the invention will become apparent to one havingordinary skill in this art.

I claim:

1. A marine structure comprising a large-diameter tubular member havingits lower end alfixed to a formation underlying a body of water andextending upwardly from said formation to a point above the surface ofthe water; a conduit member having its lower end connected to a well insaid formation and extending upwardly from said well to the surface ofthe water; said conduit member being positioned inside saidlarge-diameter member and structurally isolated therefrom continuouslyabove a point adjacent said formation, whereby vibrations induced insaid large-diameter member are prevented from being transmitted to saidconduit member; and a well head assembly mounted on said conduit memberabove the surface of the water; and a platform supported by said largediameter tubular member and isolated from said Well head assembly.

2. A marine well production facility comprising a largediameter tubularstructural member having its lower end afiixed to a formation underlyinga body of water and extending upwardly from said formation to a pointabove the surface of said water; a well conduit positioned in saidlarge-diameter member, said well conduit extending upwardly from a wellin said formation and having its upper end above the surface of thewater; a wellhead mounted atop the upper end of said Well conduit; saidwell conduit being structurally isolated from said largediameter membercontinuously above a point adjacent said formation, whereby vibrationsinduced in said large-diameter member are prevented from beingtransmitted to said Well conduit a platform supported by said largediameter tubular structural member and isolated from said wellhead, saidplatform being above the surface of the water but at a height notgreater than the position of said wellhead.

References Cited by the Examiner UNITED STATES PATENTS 1,900,163 3/1933Dana et al 166-1665 2,684,575 7/ 1954- Pyor et a1 166-665 3,015,3601/1962 Stratton -7 3,103,976 9/1963 De Vries 166-665 X 3,121,997 2/ 1964Sampson 61-46 3,201,945 8/1965 Sutton 61-465 3,209,544 10/1965 Borrmann16-465 CHARLES E. OC-ONNELL, Primary Examiner.

JACOB SHAPl-RO, Examiner.

1. A MARINE STRUCTURE COMPRISING A LARGE-DIAMETER TUBULAR MEMBER HAVINGITS LOWER END AFFIXED TO A FORMATION UNDERLYING A BODY OF WATER ANDEXTENDING UPWARDLY FROM SAID FORMATION TO A POINT ABOVE THE SURFACE OFTHE WATER; A CONDUIT MEMBER HAVING ITS LOWER END CONNECTED TO A WELL INSAID FORMATION AND EXTENDING UPWARDLY FROM SAID WELL TO THE SURFACE OFTHE WATER; SAID CONDUIT MEMBER BEING POSITIONED INSIDE SAIDLARGE-DIAMETER MEMBER AND STRUCTURALLY ISOLATED THEREFROM CONTINUOUSLYABOVE A POINT ADJACENT SAID FORMATION, WHEREBY VIBRATIONS INDUCED INSAID LARGE-DIAMETER MEMBER ARE PREVENTED FROM BEING TRANSMITTED TO SAIDCONDUIT MEMBER; AND A WELL HEAD ASSEMBLY MOUNTED ON SAID CONDUIT MEMBERABOVE THE SUR-